Pymagento

* Add `get_source`, `get_sources`, `save_source`

* Support SKUs that contain slashes

* Pass additional keyword arguments in `Magento()` to the underlying `APISession()` constructor
* Remove the `verbose` optional keyword option as well as the `log_response` parameter. Instead, use the `DEBUG` level
for logging. Instead of setting these variables to `True`, set your logger level to `DEBUG`.

* Fix `coerce_as` for list values in `get_custom_attribute`. The function now correctly gets each individual value
rather than the whole list.
* Fix type hint for list values in `get_custom_attribute`

* Remove `Magento.get_product_source_items` (deprecated since 1.3.3)
* Remove `pretty_custom_attributes` (deprecated since 1.3.4)
* Remove `log_progress` parameter to `Magento` (deprecated since 1.4.0)
* `get_custom_attribute`: add a more precise type hint on the return type

* Add `get_product_by_query`
* `set_custom_attributes`, `set_custom_attribute` and `serialize_attribute_value` now support an optional
`force_none=True` to prevent `None` values from being serialized as empty string. This can be useful to erase
attributes.
* `MagentoAssertionError` is now accessible from the `magento` module (`magento.MagentoAssertionError`)